1. Field of the Invention
The present invention relates to a flat, planar-type image display apparatus comprising an evacuated envelope, a method of manufacturing the image display apparatus, and a sealing-material applying apparatus.
2. Description of the Related Art
In recent years, display apparatuses have been developed as next-generation, lightweight, thin, planar-type displays. These apparatus comprise a phosphor screen and a number of electron-emitting elements (hereinafter called “emitters”). The emitters are arranged, opposing the phosphor screen. The emitters may be of either field emission type or surface conduction type. Display apparatuses using field emission type electron-emitting elements as emitters are generally called “field emission displays” (hereinafter referred to as “FEDs”). Display apparatuses using surface conduction type electron-emitting elements as emitters are generally called “surface conduction type electronic discharge display” (hereinafter referred to as “SEDs”).
For example, FEDs generally have a front substrate and a rear substrate opposing each other and spaced apart by a predetermined distance. These substrates constitute an evacuated envelope, because they are coupled together at their circumferential edges, with a rectangle frame-like sidewall interposed between them. The phosphor screen is formed on the inner surface of the front substrate. A number of emitters are provided on the inner surface of the rear substrate. The emitters are used as electron-emitting sources. The electrons they emit excite phosphor layers, causing the phosphor layers to emit light. A plurality of support members are interposed between the front substrate and the rear substrate to withstand atmospheric pressure applied on these substrates.
The electric potential at the rear substrate is about 0V. The anode voltage Va is applied to the phosphor screen. The electron beams emitted from the emitters are applied to the red phosphor layers, that constitute the phosphor screen, to energize the phosphor layers, whereby an image is displayed.
In such a FED, the distance between the front substrate and the rear substrate can be set at several millimeters or less. Therefore, FED is lighter and thinner than the cathode-ray tube (CRT) used at present as a display of televisions or computers.
It is necessary to maintain the degree of vacuum inside the evacuated envelope at 10−5 to 10−6 Pa in the planar display apparatus described above. In the conventional evacuation method, the surface adsorption gas inside the envelope is liberated by performing baking in which the envelope is heated to about 300° C. The evacuation method cannot completely liberate the surface adsorption gas.
Jpn. Pat. Appln. KOKAI Publication No. 9-82245, for example, discloses a planar display apparatuses of various structures. In one structure disclosed, getter material such as Ti, Zr or alloy thereof covers the metal back that is formed on the phosphor screen of the front substrate. In another structure disclosed, the metal back is made of getter material. In still another structure disclosed, getter material covers the components other than the electron-emitting elements, in the image-displaying region.
In the image display apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-82245, getter material is formed in the ordinary panel process. Inevitably, the surface of getter material will be oxidized. The getter material is highly active at the surface. Once oxidized at surface, the getter material can no longer adsorb gas as much as desired.
A method of enhancing the degree of vacuum inside the evacuated envelope may be considered. In this method, a rear substrate, a sidewall, and a front substrate are brought into a vacuum chamber. These components are baked in the vacuum atmosphere and irradiated with an electron beam. The surface adsorption gas is thereby released from the rear substrate, sidewall and front substrate. Thereafter, a getter film is formed, and the sidewall, rear substrate and front substrate are sealed together, with frit glass or the like, in the vacuum atmosphere. This method can release the surface adsorption gas sufficiently by means of electron-beam washing. The getter film is not oxidized. A sufficient gas adsorption can be accomplished. In addition, the space in the image display apparatus is not wasted because no evacuation pipes are necessary.
However, to fuse the components together in a vacuum atmosphere by using frit glass, the frit glass must be heated to a high temperature of 400° C. or more. When so heated, the frit glass generates air bubbles. This degrades the air-tightness, sealing strength and the like of the evacuated envelope. Consequently, the reliability of the image display apparatus decreases. In view of the characteristic of the electron-emitting elements, it may be desirable not to heat the frit glass to 400° C. or more. In such a case, the method of sealing the components with frit glass is not desirable.